1. Field of the Invention
This invention relates to processes for the reclamation or partial recovery of discarded fluid catalytic cracking (“FCC”) equilibrium catalyst. In particular, the invention relates to a process for reclaiming discarded FCC equilibrium catalyst (“catalyst” or “ECAT”) containing low levels of metal contaminants using the principles of magnetic separation. More particularly, the invention relates to the use of magnetic separation off-site and away from any FCC process unit or petroleum refining process for the purpose of reclaiming FCC equilibrium catalyst containing low levels of metal contaminants.
2. Background of the Invention
FCC equilibrium catalysts are used in the petroleum refining industry to convert crude oil fractions into smaller molecular weight hydrocarbon compounds. FCC catalysts are typically composed of particles of sprayed dried mixture of kaolin clay and zeolite in a silica or alumina binding agent ranging in size from approximately four microns to approximately 130 microns. A typical FCC unit contains several hundred tons of catalyst. Small FCC units may contain only fifty tons, while some larger units contain 500 or more tons. The catalyst particles circulate throughout the FCC unit at rates of 10-14 tons per minute. For example, a three-hundred ton inventory FCC unit will circulate its inventory sixty-seven times per day, at a 6.3 catalyst to oil ratio in the FCC riser reactor or at a feed rate of approximately 267,000 pounds per hour. During the cracking process, the FCC catalyst accumulates contaminants such as nickel, vanadium, iron, calcium, and various other metals. These contaminants decrease the effectiveness of the catalyst (i.e., the ability to convert crude oil fractions into desirable products). The longer the catalyst particles remain in the unit, the more metal contaminants they accumulate. Particle age is typically expressed in terms of the number of days the particle has been in the FCC unit. Thus, “older” particles (e.g., 100 days or more) have commensurately lower activity than “younger” particles (e.g., 50 days or less) that have not been in the FCC unit as long. Accordingly, older catalyst particles are unable to convert the petroleum oil effectively into consumer products.
Because of this constant loss of catalytic activity, “fresh” catalyst needs to be added to the FCC inventory to maintain the catalytic activity of the system at the required level. Thus, all FCC units periodically remove a portion of the catalyst from the FCC unit and replace it with fresh catalyst to maintain catalyst activity and to manage the metals content of the FCC catalyst inventory. For example, in some FCC units, approximately six tons of new catalyst per day is added to maintain activity. A similarly-sized fraction of used catalyst must be removed to make room for the fresh catalyst being added. Presently, catalyst that is removed from FCC units is discarded into landfills or reused in alternative applications, such as cement or asphalt filler.
A significant fraction of particles that are removed from the FCC unit each day retains catalytic activity, however. Specifically, 20-40% of the particles in any fraction of equilibrium catalyst are fifty days old or less. As previously noted, these particles have not been in the FCC unit as long as the older particles and will retain catalytic activity. Presently, however, there is no feasible mechanism to separate these younger particles containing lower metal content from the older particles that no longer have catalytic activity due to their higher metal content.
In some cases, rather than replacing the spent catalyst with completely new catalyst, the contaminated catalyst is regenerated and then recycled back into the FCC unit. Magnetic separation is one process that has been used to reclaim FCC catalyst. Magnetic separation of metals-contaminated equilibrium catalyst (ECAT) from ECAT particles having a lower metal content has previously been commercialized. See, e.g., U.S. Pat. No. 4,406,773 (Hettinger et al.); U.S. Pat. No. 5,147,527 (Hettinger et al.); U.S. Pat. No. 5,171,424 (Hettinger); U.S. Pat. No. 5,190,635 (Hettinger); U.S. Pat. No. 5,198,098 (Hettinger); U.S. Pat. No. 5,230,869 (Hettinger et al.); U.S. Pat. No. 5,328,594 (Hettinger); U.S. Pat. No. 5,364,827 (Hettinger et al.); U.S. Pat. No. 5,393,412 (Hettinger); U.S. Pat. No. 5,538,624 (Hettinger); U.S. Pat. No. 5,958,219 (Goolsby); U.S. Pat. No. 6,041,942 (Goolsby); U.S. 6,099,721 (Goolsby); U.S. Pat. No. 6,194,337 (Goolsby); and U.S. Reissue Pat. No. 35,046 (Hettinger et al.) all of which are hereby incorporated by reference. Some other work has been done in the area of magnetic separation of FCC catalyst. U.S. Pat. No. 5,250,482 (Doctor), which is hereby incorporated by reference, describes a super-cooled, quadruple open-gradient magnetic separation system to separate ECAT having more than about 2000 ppm nickel equivalents from ECAT having less about 2000 ppm nickel equivalents.
One process for recycling FCC catalyst with high metal content is the MagnaCat™ process. The MagnaCat™ process is integrated into the FCC unit and removes catalyst particles that are contaminated with high levels of metals and having high magnetic properties. The MagnaCat™ process discards 10-30% of these highly contaminated particles, while 70 to 90% of the remaining treated catalyst is recycled directly back into the FCC unit. However, only about 30% of the FCC units in the world can utilize the MagnaCat™ process due to the requirements of high metals content and the associated magnetic properties needed to effectively utilize the separation technology. This leaves about 70% of the world's FCC units that discard large amounts of catalyst daily. Thus, the majority of FCC units are unable to take advantage of the environmental benefits of the recycling process.
A significant drawback to the magnetic processes known in the art is that they require dedication of the magnetic separation apparatus to a particular FCC unit. For example, Hettinger et al. U.S. Pat. No. 4,406,773 describe the use of an electromagnetic and/or permanent magnetic separation process which is directly associated with a high carbo-metallic feed FCC process unit in order to separate the older, high metals FCC ECAT from the younger FCC ECAT and directly recycling the recovered ECAT back into the FCC regenerator of the FCC Process unit with high carbo-metallic feed FCC operation.
However, because of the requirement that the magnetic separation unit be integrated into the FCC process, refiners are presently limited in the amount of FCC catalyst they can reclaim and recycle within their company if they have more than one FCC unit. Specifically, such on-line separation systems are only able to separate and remove the oldest catalyst particles, which contain the most metal. For example, Hettinger et al., U.S. Pat. Nos. 4,406,773 and 5,147,527 require that the FCC ECAT magnetic separation be performed on ECAT having 1000 ppm to 30,000 ppm nickel equivalents of heavy metal(s) and/or metal compound(s) measured in regenerated equilibrium catalyst. Similarly, the MagnaCat™ system separates particles with magnetic susceptibility values at least as large as 5×10−6 to 10×10−6 emu/g (electron mass units per gram), Hettinger et al., U.S. Pat. No. 5,190,635. As a result, these systems are only able to remove the material having the most magnetic content, which represents approximately 10-20% of the total inventory in the FCC unit. Metals levels for these high magnetic fractions range from 1600 to 2500 ppm nickel and 6000 to 10,000 ppm iron with the magnetic susceptibilities ranging from 20×10−6 emu/g to 60×10−6 emu/g.
Moreover, because the magnetic separation systems known in the art are integrated into the FCC unit, the recycled ECAT must be reintroduced into the same FCC unit from which it was originally extracted. With the consolidation of refineries within the industry, a refinery group may want to cascade its own ECAT within its system (i.e., taking catalyst from one refinery FCC unit and adding to a different refinery FCC unit).
A still further limitation of processes that are integrated into the FCC unit is that they require an additional cooling step before the ECAT can be reclaimed. The high temperatures of an FCC unit decrease the magnetic properties of the material. In order to achieve effective magnetic separation, the material must be cooled to increase its magnetic properties. Hettinger et al. describe an elaborate cooling system that must be implemented before the ECAT can be processed. The catalyst is removed from a hot FCC regenerator at a temperature of about 900-1400° F., and under a pressure of about 10-50 pounds per square inch absolute. Handling and controlling the hot catalyst from the FCC unit under pressure can be difficult, dangerous, and expensive if not performed with the appropriate safety measures. The external surface of the catalyst transfer pipe can become red hot due to heat transfer from the catalyst before the catalyst enters the catalyst cooler, which could cause significant burns to refinery personnel if not addressed. Cooling the catalyst from 1400° F. to 300° F. is difficult and requires an expensive cooler with extensive piping and controls for the cooling medium. Erosion of the catalyst transfer pipes used to pneumatically transfer the catalyst to the process unit can also become a maintenance issue.
Also, because the reclaimed catalyst is recycled directly into the FCC unit, integrated processes require an additional line into the FCC regenerator with either a valve or continuous air to prevent catalyst from exiting the FCC unit. These lines can become plugged if the conditions or air are not monitored. As a result of these limitations, the use of these processes is strictly limited.